Tolkien is the obvious example. The Silimarillion always struck me as a worldbuilding reference forcibly turned into a story. George R. R. Martin is a modern ex

Tolkien is the obvious example. The Silimarillion always struck me as a worldbuilding reference forcibly turned into a story. George R. R. Martin is a modern example. The level of importance of world building really depends on what the goal is. I don't think h2g2 would have been majorly improved by a lot of world building, but I can appreciate the world building that's been done for Pratchett's Discworld, though that's as much a reflection on the length of that series than Pratchett's priorities